In-mold decoration (IMD) has emerged as an increasingly popular set of techniques for decorating injection-molded parts. IMD techniques are used to incorporate text, numbers, legends, other symbols and information, and purely decoratively designs into injection molded parts such as telephones and other consumer electronics, automobile dashboards, containers and packaging for consumer products, and indeed the full spectrum of injection molded parts.
IMD typically involves creating an in-mold decoration film (IMD film or IMD decorated film) comprising the image to be transferred to or integrated with a surface of the injection-molded part. In a typical in-mold transfer process, a polyethylene terephthalate (PET) film is treated with a release agent (to facilitate image transfer) and then coated with a durable layer to provide oil and scratch resistance. The decoration is then printed and/or otherwise formed on the treated and coated PET film, followed by coating the film with an adhesive (e.g., hot melt or polyurethane adhesive) to form the in-mold transfer film. The film is then inserted into the injection mold prior to injection of the molten resin, and the decoration (or other image) is transferred from the PET film to the injection-molded item. In a typical in-mold insert process, the decoration or other image is not transferred from the IMD decorated film to the injection-molded item but instead the IMD decorated film is bonded to and becomes a part of the injection-molded item. In one typical in-mold insert process, a polycarbonate (PC) substrate is used. The decoration or other image to be included on the injection-molded item is printed or otherwise formed on a surface of the PC substrate. The patterned substrate is then coated with a thin protective layer (to protect the ink from damage during the injection process) to provide the IMD decorated film.
In some cases, IMD techniques may be used to apply or incorporate into an injection-molded item a decoration or other image that comprises a patterned metal thin film or other thin film material. In one approach, such a patterned thin film design is incorporated by forming a patterned metal thin film layer on the IMD decorated film. One typical prior art approach to fabricating an in-mold decoration film comprising a patterned metal thin film involves the use of photolithographic techniques and chemical etching. The typical photolithographic process comprises several time consuming and high cost steps including (1) forming an unpatterned metal thin film layer (2) coating the metal thin film with photoresist; (3) patterning the photoresist by image-wise exposing it through a photomask to, for example, ultraviolet light; (4) “developing” the patterned image by removing the photoresist from either the exposed or the unexposed areas, depending on the type of photoresist used, to uncover the metal thin film in areas from which it is to be removed (i.e., areas where no thin film material is to be located); (5) using a chemical etching process to remove the thin film from the areas from which the photoresist has been removed; and (6) stripping the remaining photoresist to uncover the patterned thin film structures.
Certain of the processing steps under the photolithographic approach, such as the image-wise exposure, are time consuming and require careful registration and alignment of the mask and the moving target area. In addition, development and stripping of photoresist and treatment of waste from the chemical etching process may be time consuming and expensive, in addition to potentially posing an environmental hazard. The chemical etching process also tends to result in a less shiny metal surface, which is often undesirable for high-end decoration applications.
Therefore, there is a need for a process for forming patterned thin film structures on a plastic substrate for use as an IMD decorated film that does not require the use of photolithography or chemical etching.